The disclosure relates to a method for producing a piston having at least one cooling channel for an internal combustion engine that is produced from at least one upper part and one lower part, wherein the cooling channel of the piston is formed using the upper part and the lower part, and the upper part and the lower part are produced employing a forging process.
A liquid-cooled piston for an internal combustion engine is known from DE 10 2006 022 413 B4 that comprises a radially circumferential ring carrier cooling channel. The ring carrier cooling channel consists of a cooling channel spaced apart from the piston crown and a ring carrier intended to receive a piston ring, wherein the cooling channel is formed directly to the ring carrier on its internal side over its entire circumference. Further, the cooling channel includes at least one inlet orifice and at least one outlet orifice through which a cooling medium can flow in or out, respectively. The cooling channel of the ring carrier cooling channel, produced without machining, has a geometrically structured wall for stiffening that includes geometrically identical and repeating or alternating structures facing inward, wherein the cooling channel has formed ribs on the inner wall offset to each other and extending in a cross-sectional plane across the entire inner wall of the annular channel.
The disadvantage of this type of piston for an internal combustion engine known from the prior art is that the ring carrier cooling channel for stiffening is complex and therefore expensive to produce. The result is increased production costs for a piston that has a ring carrier cooling channel with a geometrically structured wall.
It would be desirable to create a potential by means of which a piston can be produced simply and cost-effectively and which avoids the aforementioned disadvantages.
This potential is achieved by additionally forging at least one rib-like element, specifically at least one rib, at the same time as the forging of the upper part in one area of the cooling channel of the upper part, and/or during the forging process for the lower part in one area of the cooling channel, at least one rib-like element, specifically at least one rib, is also forged. A fully forged cooling channel shape is thusly created.
An alternative way of achieving this potential is that during the forging of the upper part in one area of the cooling channel of the upper part at least one additional rib-like element, in particular at least one rib, is forged at the same time.
A further alternative is that during the forging of the lower part in one area of the cooling channel of the lower part at least one rib-like element, specifically at least one rib, is forged at the same time.
It is advantageous that cost-effective production of the piston by means of this method is possible by forging rib-like elements in the form of stiffening or reinforcing ribs directly during the forging process for the upper part and/or the lower part in the area of the cooling channel. Machining of the cooling channel cavity can be dispensed with after the upper part and/or the lower part of the piston is forged. Because both the reinforcements in the area of the cooling channel are forged simultaneously with the forging of the attendant upper and/or lower part, net shape forging is possible. In addition, it is possible using the method to optimize cooling of the piston during operation in an internal combustion engine. As a result of the enlarged surface resulting from the shape of the rib-like elements formed as cooling ribs in the cooling channel, improved cooling efficiency in the piston is possible. Furthermore, the flow of coolant in the piston and its movement in the piston is improved so that cooling efficiency in the piston is also improved as a result. It is further advantageous that the cooling channel is stiffened as a result of the rib-like elements in the area of the cooling channel, specifically the cooling channel crown is stiffened. Piston deformation during operation of the piston in an internal combustion engine can be reduced. As a result of the stiffening in the form of rib-like elements in the area of the cooling channel crown, an improved stress situation in the area of the cooling channel crown is achieved. The cooling channel crown is the area of the piston that forms a maximum in the cooling channel with reference to the piston stroke axis towards the combustion chamber, where the cooling channel crown is usually the highest point in the cooling channel and thus lies in the area of the upper part. The piston produced in accordance with the method has high ignition pressure load capacity with simultaneous good cooling of the piston with and without bracing of the outer ring zone. In addition, pistons with a lower compression height can be produced.
The rib-like element can be forged perpendicular to the circumferential direction of the cooling channel. By forging the rib-like element into the cooling channel perpendicular to the circumferential direction of the piston cooling channel, it is possible, for example, for the flow of coolant, cooling oil for example, entering the cooling channel by means of an inlet orifice during operation of the piston in an internal combustion engine to be speeded up or slowed down optimally because of the perpendicular forging until the coolant leaves the cooling channel by means of an outlet orifice. Improved cooling of the piston during operation is possible by means of the speeding up or slowing down of coolant flow. If the cooling channel has several rib-like elements that are forged in the appropriate upper part and/or appropriate lower part perpendicular to the circumferential direction of the cooling channel, the resulting arrangement with reference to the piston center point is a star shape.
The upper part and the lower part can be connected by means of a joining process, specifically by means of friction welding, to produce the piston. As a result, it is possible that the area below a combustion bowl of the piston and the area in which the later ring grooves are located can be joined optimally and simply. The piston can thus be produced easily and cost-effectively.
When forging the upper part and/or the lower part, at least two weld supports are forged at the same time, specifically an external support and a central support. An external support is the area that is located in the area of the later ring grooves and connects the outer sides of the piston, i.e. the outer side of the upper part and of the lower part. The external support is at a constant radial distance completely circumferential around the piston stroke axis of the upper part and the lower part. A central support is a central area of the piston around the piston stroke axis, in which the piston upper part is also joined to the piston lower part. The central support is also known by the term “central link”.
The upper part and the lower part thus lie on top of each other in the area of the external support and in the area of the central support and are joined simultaneously by means of friction welding in the area of the external support and of the central support. In the respective area of the weld support, a weld plane is formed, where the weld plane of the external support and the weld plane of the central support may lie in the same weld plane or may lie in different weld planes. It is further possible that the respective weld planes of the external support and of the central support are executed curved and/or flat when the piston is produced. By means of the central support in particular, it is possible to vary the weld plane geometry so that the load-critical friction weld seams are positioned in non-critical load planes of the subsequently produced piston.
The weld plane is not restricted to a flat surface but refers to a plane that may follow any kind of course. Several weld planes can be combined into a single, common weld plane, where the course of the individual, common weld plane is compose of the course of the several weld planes.
Following the joining of the upper part and lower part, the cooling channel of the piston is formed between the central support and the external support.
In an advantageous aspect, the piston consists of a steel material. Alternatively, it is possible that the piston consists of a light-alloy material, for example, aluminum, an aluminum alloy, a magnesium alloy, or similar. It is further possible that the piston, consisting of an upper part and a lower part, consists of different materials, for example, the upper part consists of a steel material and the lower part of a light-alloy material (or conversely).
In a further aspect, the piston has at least one rib-like element, specifically at least one rib, in the cooling channel. If the cooling channel of the piston has several rib-like elements, it is possible that the elements are shaped geometrically the same in the piston, i.e. the elements have recurring geometrical structures and/or shapes. Alternatively, or supplementally, it is possible that the rib-like elements in the cooling channel have alternating structures and/or shapes.
A geometrically identical structure is given, for example, if the distance between the rib-like elements in the cooling channel is the same with reference to the radial periphery in the piston. An alternating structure is given, for example, if the array of rib-like structures in the cooling channel is arranged with a different distance to each other in the radial periphery of the cooling channel so that areas with a higher density of rib-like elements and areas with a lower density result. A recurring geometrical design, for example, is formed in the piston when the rib-like elements all have the same shape. An alternating design is formed in the piston, for example, when the rib-like elements each has a different shape.
It is furthermore possible that the rib-like elements extend out of the cooling channel so that a type of elevation results in the cooling channel, or alternatively extend into the cooling channel so that valleys result in the cooling channel. Furthermore, it is alternatively possible that some rib-like elements in the cooling channel extend into the cooling channel and other rib-like elements project out of the cooling channel. The elevations and valleys may have an identical or alternative geometrical structure and/or design in accordance with the previous description.
The rib-like element can be configured as a rib, where as an alternative to a rib, a pressure area, a depression, a recess, a seam, a bead, ribbing or similar is possible.
In a further aspect, a rib-like element is disposed diagonally to the direction of the cooling channel circulation.
In a further aspect, the piston has at least two weld supports, specifically an external support and a central support that each has at least one weld plane, wherein the weld plane of the upper part and of the lower part are located in the area of the external support and in the area of the central support in the same weld plane or are located in different weld planes.
In a further aspect, the weld plane in the area of the external support and/or in the area of the central support in the piston is executed curved and/or flat.